Such a system for controlling an operating parameter of an internal combustion engine is well known for the idling speed control of engines from U.S. Pat. No. 4,441,471. There, it is suggested that for the control of the idling speed, an electrically operated actuator, which has an effect on this operating parameter, is triggered via a PID-controller in such a way that the idling speed, as the operating parameter to be controlled, takes on a predetermined desired value. Furthermore, a limiting controller is provided for the speed and temperature dependent limitation of the actuator trigger signal, this limiting controller affecting the PID-controller in the sense of a maximum or minimum limitation of the trigger signal.
Systems which are difficult to control cannot be satisfactorily controlled by a PID-controller with respect to accuracy of control, dynamics and/or stability. These systems are found for example in the use of actuators which have highly variable frictional forces over the controlling range and also have torques which oppose the control movement with specimen dispersions and temperature drifts additionally playing a role.
It is thus the task of the invention to specify measures which ensure satisfactory control of an operating parameter in an internal combustion engine, even in the case of systems which are difficult to control. This is achieved in that, with predetermined conditions being present, the rate of change of the operating parameter to be controlled can be adjusted to a predetermined value by means of intervention in the integration process and/or in the proportional amplification process.
From U.S. Pat. No. 4,947,815, an actuator for the controlled supply of combustion air to an internal combustion engine is known, which actuator is equipped with a return spring against which a counterspring acts in order to set a predetermined rest position. This actuator counteracts an adjusting movement in the different areas of its adjustment travel by means of various forces or torques.
British Pat. 1,603,921 describes a control system for the position control of a throttle flap of an internal combustion engine in dependence upon the accelerator pedal position, a so-called electronic accelerator. In order to improve the exhaust-gas composition, the level of the output signal of the position controller is limited. With a fast change in the accelerator pedal position, this leads to a limit on the rate of change of the throttle flap and also leads to an improvement of the composition of the exhaust gas in the transition range.